A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphalt shingle material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt strip material, either an organic felt or a glass fiber mat is passed through a coater containing liquid asphalt to form a tacky asphalt coated strip. Subsequently, the hot asphalt strip is passed beneath one or more granule applicators which apply the protective surface granules to portions of the asphalt strip material.
Often, in the manufacture of shingles, at least two types of granules are employed: 1) headlap granules which are granules of relatively low cost for portions of the shingle which are to be covered up; and 2) prime granules which are granules of relatively higher cost and are applied to the portions of the shingle which will be exposed on the roof. It is to be understood that the term “prime” granules generally includes both highlighted colored blend drop granules and background granules.
Not all of the granules applied to the hot, tacky, asphalt coated strip adhere to the strip, and, typically, the strip material is turned around a slate drum to invert the strip and cause the non-adhered granules to drop off. These non-adhered granules, which are known as backfall granules, are usually collected in a backfall hopper. The backfall hopper dispenses a continuous supply of the “backfall” granules onto the sheet.
To provide a color pattern of pleasing appearance, the shingles are provided in different colors, usually in the form of a series of granule discharges of different colors or different shades. These highlighted series of discharges, referred to as blend drops, are typically made by discharging granules from a series of blend drop granule dispensers. To produce the desired effect, the length and spacing of the blend drops must be accurate. The length and spacing of each blend drop on the sheet is dependent on the relative speed of the sheet and the length of time during which the blend drop granules are discharged.
After discharging the highlighted blend drop granules, an oversupply of background granules is applied to the sheet. In making asphalt shingles, the standard method of prime granule application is to provide a continuous “curtain coater” application of background granules at a backfall hopper. While this method ensures that no surface of the shingle is uncovered, it also results in the already covered blend drop areas receiving 2 to 4 layers of granules (with 1 layer equaling the quantity of granules that sticks to the asphalt coated surface).
This excess amount of background granules is recovered by allowing both the prime and background granules to fall into a backfall hopper during the shingle making process. The backfall hopper has separate compartments that are in general alignment with the areas of the shingle that receive the different types of granules; i.e., the headlap granules and the prime granules. However, in order to ensure that the less expensive background granules are not mixed into the more expensive prime granules, the “prime granule” compartment of the backfall hopper is narrower than the corresponding width of the prime area of the shingle. When the granule covered sheet is passed over a slate drum, only excess prime shingles fall into the narrower prime granule compartment, thus allowing for the recycling of “prime only” granules.
It is desired to provide an improved method and apparatus for discharging background granules onto the moving sheet to produce a uniform distribution of granules without wasting prime background granules.
It is particularly desirable to provide a more efficient and consistent granule discharging system that is more responsive to changes in line speed of the asphalt coated sheet, particularly at the higher line speeds.
Also, it would be helpful to have a granule discharging system with a more accurate control of the discharging of the background granules to provide improved blend drop appearance.